In the title compound, C19H23N3OS, the two fused rings of the thieno[2,3-d]pyrimidin-4(3H)-one system are almost coplanar. The packing of the molecules in the crystal structure is determined by van der Waals forces. No intermolecular hydrogen-bonding interactions or π-π stacking interactions are present in the crystal structure. © 2006 Internatio...